Progress toward a low-noise temperature regulation using a superconductive high-T/sub c/ microbridge

Our results measuring I-V characteristics of YBCO/MgO microbridges show that large current sensitivities (10 mA/K) as a function of temperature can be obtained, roughly independently of the applied voltage V up to a few hundred mV. This offers the possibility of working with high values of the dynamic resistance so that the phonon noise associated to the thermal boundary resistance, located at the YBCO/MgO interface, becomes dominant. A noise equivalent temperature of 10/sup -8/ K//spl radic/Hz (T=85 K, f>1 kHz) has already been obtained in a 0.2/spl times/12/spl times/10 /spl mu/m/sup 3/ microbridge. We describe a process involving the periodical sampling of the I-V characteristics that eliminates 1/f amplifier noise and returns the current value (temperature dependent) at fixed voltage bias (/spl plusmn/1 mV). This output, locked to a reference voltage through a commercial temperature regulator, leads to temperature fluctuations less than 100 /spl mu/K/sub pp/ in a 10 Hz bandwidth. These results are promising to enhance performances of high-T/sub c/ microbolometers as infrared detectors.<
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